Solved several bugs:

  * New nodes are first linked before adding them to the lane. This avoids using invalid lane end positions.
  * In the get_start_point() and get_end_point() functions: the lane object address is compared instead of the lane ID.
  * In the get_start_point() and get_end_point() functions: for left lanes, the last node is used instead of the first one to get the desired point.